I suppose you are misunderstanding me on purpose, but let me try again in very clear terms anyway: Offering the same service or product (a specific flight if you will, a chunk of butter of the same brand in the same store at the same time) to two independent customers at different prices based on prior knowledge about them unrelated to the specific good or service is fundamentally unjust.

What you are referring to is 'price discrimination'[1]. @alex43578 is correct in his examples. In the 'Uber/Lyft' example, his metric for service similarity in the case of a ride to the airport vs. the middle of nowhere can be seen in the distance driven. The problem is that arguments can always be made on why pricing one demographic vs another makes business sense.

In the case of Uber/Lyft, the company can say a ride to the middle of nowhere costs more than a hotspot destination because the odds of finding someone hailing another ride from there are low. This would mean the driver would have to spend more on gas picking up their next customer. Although this seems reasonable, it's probabilistic in nature. This may also not be the case, but the company must price this risk to keep their drivers happy. Well what of the case where the destination is a dangerous neighborhood where the driver feels like their life will be in danger? How do we price the risk then? And that says nothing about the possible mismatch of perception between the seller and the customer.

How about if a grocery store sells goods at a higher price to customers in lower income areas because they notice that it lowers the number of high income area customers to the point they make less profit? Is it right for that store to raise the price for identifiably lower income area customer to make up for the lost profit?

> Offering the same service or product (a specific flight if you will, a chunk of butter of the same brand in the same store at the same time) to two independent customers at different prices based on prior knowledge about them unrelated to the specific good or service is fundamentally unjust

Your statement includes things like loyalty programs and memberships. Presenting these credentials at checkout means customers are willingly giving the company "prior knowledge about them" (that they've shopped at the store before and how much they're willing to spend) unrelated to the *specific* food or service they're purchasing. Should these practices be allowed?

The point of this reply isn't to say what should or shouldn't be allowed, it's to show that I believe the issue is more nuanced than you can account for in your statement of what constitutes unjust business practices.

[1] https://en.wikipedia.org/wiki/Price_discrimination

Why is it unjust? It’s absolutely the store or individual’s choice to charge what they want to who they want, assuming that they aren’t discriminating against a protected class.

In your example, why aren’t all prices then fixed between different stores to ensure justice? Whole Foods shouldn’t be allowed to charge more than Discount Food Bin for the same can of beans, and WF in Oakland shouldn’t charge less than WF in Marin.